The present invention generally relates to a semiconductor device and a method for fabricating the same. More particularly, the present invention relates to a semiconductor device including a capacitor device having a capacitive insulating film of insulating metal oxide film such as a ferroelectric film or a high dielectric film (i.e., a film made of a material having a high dielectric constant) and to a method for fabricating the same.
In recent years, as various electronic units such as microcomputers operating at an even higher speed and with even lower power consumption have been developed, the performance of consumer-use electronic units have also been further enhanced. Correspondingly, the sizes of semiconductor devices used for these units have also been rapidly reduced drastically.
As semiconductor devices have been miniaturized, unwanted radiation, i.e., electromagnetic wave noise generated from electronic units, has become a serious problem. Technology for incorporating a large-capacity capacitor device, including a ferroelectric film or a high dielectric film as a capacitive insulating film, into a semiconductor integrated circuit is now the object of much attention as a means for reducing the unwanted radiation.
On the other hand, since a very highly integrated dynamic RAM is now provided, researches have been widely carried out on technology for using a high dielectric film as a capacitive insulating film, instead of a silicon oxide film or a silicon nitride film, which has been conventionally used.
Furthermore, in order to put into practical use a non-volatile RAM operating with a low voltage and enabling high-speed write and read operations, researches and developments have also been vigorously carried out on a ferroelectric film having spontaneous polarization properties. A ferroelectric memory using a ferroelectric film as a capacitive insulating film takes advantage of a phenomenon that the amount of charge flowing into/out of a data line of a ferroelectric memory differs depending upon whether or not the spontaneous polarization of the ferroelectric film is inverted.
In all of these types of semiconductor devices mentioned above, it is an urgent task to develop technology for realizing very high integration for a capacitor device without deteriorating the characteristics thereof.
Hereinafter, a conventional semiconductor device will be described with reference to FIG. 13.
FIG. 13 illustrates a cross-sectional structure of a conventional semiconductor device. As shown in FIG. 13, a lower electrode 2 made of a first platinum film, a capacitive insulating film 3 made of a ferroelectric film and an upper electrode 4 made of a second platinum film are formed in this order on a semiconductor substrate 1 made of silicon. The lower electrode 2, the capacitive insulating film 3 and the upper electrode 4 constitute a capacitor device. An interlevel insulating film 5 made of a silicon oxide film, a silicon nitride film or the like is deposited to cover the entire surface of the semiconductor substrate 1 as well as the capacitor device. A lower-electrode contact hole 6 and an upper-electrode contact hole 7 are formed through the interlevel insulating film 5. Metal interconnections 8, each consisting of a titanium film 8a, a first titanium nitride film 8b, an aluminum film 8c and a second titanium nitride film 8d, are formed to cover the interlevel insulating film 5 as well as the inner surfaces of the lower-electrode contact hole 6 and the upper-electrode contact hole 7.
Hereinafter, a method for fabricating the conventional semiconductor device will be described with reference to FIGS. 14(a) through 14(e).
First, as shown in FIG. 14(a), the first platinum film 2A, the ferroelectric film 3A and the second platinum film 4A are sequentially stacked over the entire surface of the semi-conductor substrate 1. Thereafter, as shown in FIG. 14(b), the second platinum film 4A is selectively etched, thereby forming the upper electrode 4. Then, in order to recover and stabilize the crystal structure of the ferroelectric film 3A, the ferroelectric film 3A is subjected to a heat treatment within oxygen ambient.
Next, as shown in FIG. 14(c), the ferroelectric film 3A and the first platinum film 2A are selectively etched, thereby forming the capacitive insulating film 3 out of the ferroelectric film 3A and the lower electrode 2 out of the first platinum film 2A. Then, in order to recover and stabilize the crystal structure of the ferroelectric film constituting the capacitive insulating film 3, the capacitive insulating film 3 is subjected to a heat treatment within oxygen ambient.
Subsequently, as shown in FIG. 14(d), the interlevel insulating film 5 made of a silicon oxide film or a silicon nitride film is deposited over the entire surface of the semi-conductor substrate 1. And the lower-electrode contact hole 6 and the upper-electrode contact hole 7 are formed through the interlevel insulating film 5. Then, in order to recover and stabilize the crystal structure of the ferroelectric film constituting the capacitive insulating film 3, the capacitive insulating film 3 is subjected to a heat treatment within oxygen ambient.
In order to prevent the lower electrode 2 or the upper electrode 4 from being oxidized as a result of the reaction between the lower electrode 2 or the upper electrode 4 with the capacitive insulating film 3 during the heat treatment conducted to recover and stabilize the crystal structure of the ferroelectric film, the lower and the upper electrodes 2, 4 are made of platinum, which is hard to react with the ferroelectric film 3A constituting the capacitive insulating film 3 during the heat treatment and exhibits anti-oxidation properties even at a high temperature.
Then, as shown in FIG. 14(e), the titanium film 8a, the first titanium nitride film 8b, the aluminum film 8c and the second titanium nitride film 8d are sequentially deposited to cover the entire surface of the semiconductor substrate 1 as well as the inner surfaces of the lower-electrode contact hole 6 and the upper-electrode contact hole 7, thereby forming the metal interconnections 8, each consisting of the titanium film 8a, the first titanium nitride film 8b, the aluminum film 8c and the second titanium nitride film 8d. The titanium film 8a functions as an adhesive film for improving the adhesion between the aluminum film 8c and the platinum film constituting the upper electrode 4. The first titanium nitride film 8b functions as a barrier film for preventing aluminum in the aluminum film 8c from diffusing into the capacitive insulating film 3. The second titanium nitride film 8d functions as an anti-reflection film while an upper inter level insulating film deposited over the metal interconnections 8 is etched.
Next, in order to further improve the adhesion between the titanium film 8a constituting the metal interconnections 8 and the interlevel insulating film 5, the metal interconnections 8 are subjected to a heat treatment.
However, during the heat treatment conducted to stabilize the crystal structure of the ferroelectric film, the platinum film constituting the upper electrode comes to have column like crystal structure. Thus, during the heat treatment conducted to improve the adhesion between the metal interconnections and the interlevel insulating film, the titanium atoms in the titanium film constituting the metal interconnections adversely pass through the grain boundary of the column like crystals of the platinum film constituting the upper electrode so as to diffuse into the capacitive insulating film. As a result, since the composition of the ferroelectric film or the high dielectric film constituting the capacitive insulating film is varied, the electrical characteristics of the capacitor device are disadvantageously deteriorated.
It is not only when the upper electrode is made of platinum but also when the upper electrode is made of iridium, ruthenium, rhodium, palladium or the like that the upper electrode ordinarily has a column like crystal structure. Thus, in the latter case, the titanium atoms in the titanium film constituting the metal interconnections also adversely pass through the grain boundary of the column like crystals constituting the upper electrode so as to diffuse into the capacitive insulating film.